Position indicator for rotary element



March 5-, 1968 Y J. M. BELL 3,372,260

POSITION INDICATOR FOR ROTARY ELEMENT Filed Oct. 19, 1965 Clo/M M- @3544;

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United States Patent O 3,3723% PGSITIGN ENDHCATGR FER ROTARY ELEMENT .lolm M. Bell, Altadena, @Ialifl, assignor to Victoreen instrument Company, (lleveland, Ohio, a corporation of (Dhio Filed Oct. 1a, 1955, Ser. No. 497,992 8 Claims. (Cl. 2%--167) ABSTRACT @F THE DESULGSURE The rotary position of an element, typically a thumbwheel switch, is indicated visually by mounting symbols at corresponding positions on a cylindrical shell that rotates wth the element; illuminating the symbol at a fixed postion; and projecting a optical image of the illuminated symbol onto a diametrically opposite translucent screen. The optical projecting system is typically contained within the shell, but can greatly magnify the symbol, providing clearly readable indication even of closely spaced angular positions.

This invention has to do generally with manually adjustable devices that are rotatable to control a variable quantity, such as an electrical resistance, a spring tension, or the angle of a movable arm, for example. More precisely, the invention has to do with means for visually indicating which of its possible positions, discrete or continuously variable, the adjustable device occupies at any time.

The invention is useful, for example, for visually displaying a numeral that represents the existing position of a manually rotatable switch, typically of the panelmounted type commonly referred to as a thumbwheel switch. Such switches may be employed for many purposes, for example as an input device for controlling an input variable such as an electrical resistance supplied to an analogue computer or other system. For supplying such a resistance it is convenient to employ several decade resistance arrays connected in series, with separately actuable switches for each decade, and to display a numeral for each decade corresponding to its actual setting. The total input resistance, or other quantity, can then be read directly as a decimal number comprising the digits of the respective switches.

Such switch assemblies are commonly controlled by thumbwheel drums or disks rotatable on a common horizontal axis and each carrying the numerals through 9 on their peripheral surfaces. Such control drums may be mounted behind a panel provided with windows through which only one numeral on each drum is visible. That arrangement permits the horizontal row of digits to be seen close enough together to be read easily as a single number. However, the maximum size at which each digit can be displayed is sharply limited by the diameter of the drums.

An important object of the present invention is to overcome that limitation, so that for a given drum diameter the size of the displayed numeral can be greatly increased. That is accomplished by utilizing optical projection for displaying the positional numerals. The mechanical configuration and the optical arrangement provided by the present invention are distinctively different from prior art attempts to utilize optical projection for related purposes, leading to a more compact, economical and efiicient product. in particular, only a minimum of space is required outside of the actual control wheel itself.

A further advantage of the invention is that the alternative positions of the thumbwheel may be grouped within a relatively small angular range of rotation without loss 3,3723% Patented Mar. 5, 1968 of clarity of indication. A smaller rotational angle is then required to shift the thumbwheel between two positions, especially between positions 0 and 9 in devices that do not permit complete rotation of the control. That greatly facilitates manual operation of the switch.

In one illustrative form of the invention, a cylindrical shell of translucent material is mounted for rotation with the thumbwheel device. Numerals are carried on one sector of that shell, and are projected optically onto the diametrically opposite sector. Optical means for illumination and projection of the numerals are fixedly mounted outside and inside, respectively, the shell surface. 'With that arrangement very considerable magnification of the numerals is readily attained.

Whereas the invention is especially useful in decade devices in which the indication is in terms of decimal numerals, other number systems can also be employed, or the positions may be indicated by symbols of any desired type other than numbers. For example, a calibrated scale of any desired type may be employed in connection with a fixed reference index for indicating continuous rotation of the control element.

A full understanding of the invention and of its further objects and advantages will be had from the following description of certain illustrative manners in which it can be carried out. The particulars of that description and of the accompanying drawings which form a part of it are intended only as illustration and not as a limitation upon the scope of the invention, which is defined in the appended claims.

In the drawings:

FIG. 1 is an exploded perspective representing an illustrative thumbwheel switch embodying the invention;

FIG. 2 is a plan, partly broken away, showing the device of FIG. 1 in horizontal position with cover removed;

FIG. 3 is a section on line 3-3 of FIG. 2 with cover in position; and

FIGS. 2A and 3A are details corresponding to portions of FIGS. 2 and 3, respectively, and representing a modification.

The device illustrated in FIGS. 1 to 3 comprises an elongated main housing it of rectangular transverse section with longitudinal axis 11, a flat bottom wall 16, side walls 17 and a removable cover 12 normally secured in place by the screws 13. A fiat mounting plate 18 is removably mounted on side walls 17 inside the cover and parallel to bot-tom wall 16, defining a main housing chamber 21. Plate 18 is retained by the internal shoulder 15 on the cover (FIG. 3) and is secured by the screws 19 which work in circumferentially slotted apertures 23 in the plate, permitting convenient rotational adjustment of the plate about thumbwheel axis 22.

The thumbwheel 2G is rotatably mounted within chamber 21 on the axis 22 perpendicular to mounting plate 118. Thumbwheel 26 is of hollow, generally cylindrical form, with notched finger flanges 24 at both axial edges of its periphery to facilitate manual rotational adjustment. Between those flanges extends a cylindrical shell formation 26, typically of translucent plastic material. One axial face of thumbwheel 20 is closed by the circular disk 28, in which the shaft 30 is coaxially mounted. The other axial face is essentially open, except for the internal radial flange indicated at 29. Shaft 30 is journaled in a bore in mounting plate 18, and the wheel is freely guided axially by housing wall 16 and the parallel inner face of plate 18. At the forward end of housing 10 is a rectangular open window 14, through which a portion of the wheel periphery projects slightly, so that finger flanges 2 are accessibio for manipulation and a limited sector 27 of shell 26 is visible from outside the housing. Channels 32 are shown in the housing exterior to facilitate mounting a row of devices in a rectangular aperture in a panel.

Cover 12 is internally recessed to form a chamber 34 between the cover wall and the outer face of mounting plate 18. The rotary switch 40 is mounted in that chamber coaxially of thumbwheel 20, representing any desired device to be operated by the thumbwheel. Electrical connections for switch 40, not explicitly shown, may be provided in any desired manner, as via a conventional connector Which may be mounted in a side wall of the housing as indicated at 42. Shaft projects upward through mounting plate 18 and is squared to mate with the rotatable element of switch 40. A more complex coupling device may be employed if desired between shaft 30 and the device to be controlled by the thumbwheel, such as a gear box or linkage, as indicated schematically at 46 in FIG. 1.

A detent device is preferably provided to limit the thumbwheel angle to definite discrete positions that correspond to the operating positions of switch 40. Such a detent is illustrated by the spring 36 which is mounted on pins 37 set in mounting plate 18 and engages camming notches 38 formed at the desired angles in the circumferential channel 33 in thumbwheel disk 28. A typical decade switch requires ten notches 15 apart, making a total operating range of 135 for the thumbwheel rotation. Positive stop abutments may be provided to limit the rotation to that operating range, as illustrated by the fixed pin 39 working in the arcuate recess in the Wheel flange. If device 40 is continuously rotatable, as a conventional potentiometer, for example, a detent device is normally not required.

The projection system of the present invention is alined with the longitudinal axis 11 of housing 10 and comprises a light source 50, which is typically a small incandescent lamp mounted on a bored plate 52 which forms the rear end wall of housing 10. Light from source is directed by the condensing lens 54 onto a limited portion 65 of shell 26 of the thumbwheel in a radially inward direction. The symbols to be displayed for indication of the thumbwheel position are mounted on thumbwheel shell 26 in such position that for each angular position of the wheel the corresponding symbol lies in the light beam at 65. The symbols are formed as areas of differential light transmission, typically comprising transparent areas on a dense black ground, but may be black on a white ground if preferred. The symbols may conveniently be formed by conventional photographic procedures on a strip of photographic film which is then mounted, as by suitable adhesive, on the inner face of shell 26 at the required angular position. Such a film is indicated somewhat schematically at 66 with symbols 68. Light transmitted by the symbol at the illuminated shell surface is received by the objective lens 58. That lens forms an optical image 70 of the illuminated symbol on the diametrically opposite portion 27 of the shell within window 14.

The lenses 54 and 58 are typically mounted in respective barrels 55 and 59, which are supported in turn in suitable molded mounting formations 56 and 60 that may be formed integrally with housing 10. The lens barrels may be retained by leaf springs 62 and screws 63. Condensing lens 54 is mounted outside of thumbwheel 20, while projecting lens 58 is within that wheel between the wheel axis 22 and the illuminated portion 65 of shell 26. The degree of magnification of the image with respect to the symbol at 65 is directly controllable by the position of lens 58, the magnification varying inversely with the separation of the lens from the illuminated shell. The focal length of the lens is selected with regard to that lens position and, of course, to the shell diameter to produce a sharp image at 70. Accurate focal adjustment of lens 58 is obtained after assembly of the device by moving the lens against the friction of spring 62, as by insertion of a tool through the opening 72 in case wall 16 (FIG. 3) to engage channel 73 in the lens barrel. The projected numerals or other indicia may be accurately centered in window 14 by rotational adjustment of mounting plate 18, which carries with it both the switch assembly and the thumbwheel. Light shields 61 may be formed integrally with the housing to protect the screen at Window 14 from stray light.

It will be understood that as thumbwheel 20 is rotated different portions of the symbol carrying film enter the light beam at 65, and also different portions of translucent shell are positioned in window 14 to receive the projected symbol image. However, the shell areas that occupy the window for adjacent wheel positions typically overlap considerably, since the projected image subtends a larger angle at axis 22 than do the individual symbols on film 66, due to the optical magnification. As an illustration, each symbol on the film may subtend an angle of 15 at axis 22, While the projected image typically subtends an angle of 45 to 60. The ten digits then occupy about of the entire shell, while the projected images, due to the overlap just described, occupy about to The shell surface on which the symbols 68 are mounted and the screen surface on which they are projected need not comprise parts of a single continuous cylindrical shell, but may, for example, differ in radius, in material and in other characteristics, as required. Alternatively, the projected images may be displayed on a screen that is fixedly mounted on housing 16, as represented at 74 in FIGS. 2A and 3A diametrically opposite to the illuminated symbol-carrying shell portion and essentially parallel thereto.

Many other changes may be made in the particular illustrated structures without departing from the proper scope of the invention, which is defined in the appended claims.

I claim:

1. A system for visually indicating the position of a rotatable device, said system comprising in combination a cylindrical shell mounted for rotation about its axis and rotationally coupled to the device,

a plurality of symbols carried by the shell and comprising areas of differential light transmission, said symbols being angularly distributed to correspond to respective angular positions of the device,

means for illuminating the radially outer face of the shell at the symbol that corresponds to the existing position of the device, a portion of the illumination being transmitted radially inward through the shell by the differential transmission of the illuminated symbol,

structure forming a translucent surface diametrically opposite the illuminated portion of the shell and generally parallel thereto,

and optical means radially inward of the shell in the path of said transmitted light for projecting a real image of the illuminated symbol radially outward onto the translucent surface for visual observation from the radially outer side thereof.

2. A system as defined in claim 1, and wherein said translucent surface is formed on a portion of the cylindrical shell angularly outside said range.

3. A system for visually indicating the position of a rotatable device, said system comprising in combination a cylindrical shell mounted for rotation about its axis and rotationally coupled to the device,

a plurality of symbols carried by the shell at angularly distributed positions within an angular range of less than 180, said symbols being visible from within the shell and corresponding to respective angular positions of the device, the shell surface diametrically opposite said symbols being translucent,

means for illuminating the symbol that corresponds to the existing position of the device,

and optical means within the shell for projecting a real image of the illuminated symbol on an optical axis substantially diametrical with respect to the shell onto said translucent surface for visual observation from the radially outer side thereof.

4. A rotary switch assembly, comprising in combination structure forming a housing having a window,

a cylindrical shell mounted in the housing for rotation about the shell axis through an angle less than 180", the shell having a translucent angular portion visible at the window,

rotary switch means mounted in the housing and rotationally coupled to the shell for rotation to a plurality of discrete switch positions,

a plurality of symbols carried by the shell and visible from within the shell, said symbols corresponding to the respective switch positions and being so distributed angularly of the shell that the symbol corresponding to the existing switch position is diametrically opposite the window,

means for illuminating the symbol that is diametrically opposite the window,

and optical means within the shell for projecting a real image of the illuminated symbol on an optical axis substantially diametrical with respect to the shell onto said translucent surface at the window for visual observation from outside the housing.

5. A rotary switch assembly as defined in claim 4, and wherein said optical means comprise a lens mounted for translational movement longitudinally of the housing axis, means frictionally opposing lens movement, and means accessible from outside the housing for manually adjustably moving the lens to focus said image.

6. A rotary switch assembly as defined in claim 4, and wherein said shell includes a rim portion that is accessible at the window for manual rotation of the shell and switch means.

7. A rotary switch assembly comprising in combination structure forming a housing having a housing axis and a window lying on the axis,

a support mounted within the housing for rotational adjustment about a movement axis perpendicular to the housing axis,

a cylindrical shell mounted in the housing for coaxial rotation about the movement axis through a limited angular range less than 180, the shell having a translucent portion that is visible at the window,

rotary switch means mounted on the support and rotationally coupled to the shell,

detent means defining a plurality of discrete rotational positions of the shell and the switch means relative to the support,

means for illuminating an area of the shell on the housing axis diametrically opposite said visible portion,

optical means mounted on the housing structure Within the shell for projecting a real image of the illuminated area onto said visible portion of the shell,

and a plurality of symbols carried by the shell and visible from within the shell, said symbols corresponding to the respective switch positions and being so distributed angularly of the shell that the symbol corresponding to the existing switch position lies in the illuminated area.

8. A rotary switch assembly as defined in claim 7, and

wherein said illuminating means comprise means for directing light radially inward toward the shell on the side thereof remote from the window,

said symbols comprising areas of differential light transmission.

References Cited UNITED STATES PATENTS 2,850,942 9/1958 Stevenson et a1. 88-24 3,222,465 12/1965 Huntress et a1. 200-46 7 3,2-86,5 85 11/ 1966 McCullough et al 88-24 ROBERT K. SCHAEFER, Primary Examiner.

H. O. JONES, Assistant Examiner. 

